Incorporation of Proximally Actuated Elastically Loaded Scissors Mechanism for the Leg Design of a Quadruped Robot

Abstract

Spring Loaded Pantographs (SLPs) are mechanisms that are often incorporated in the design of lightweight legs for multi-legged robots. This is due to the fact that natural quadruped (Four-Legged organisms) tend to keep the subsequent proximal and distal seqments, of a 3-segment leg, mostly parallel during their locomotion. Cable-pulled SLP legs have proven to be highly agile, robust and also depict energy storage capabilities. However, In such designs the extension of the distal segments via the knee joint of the leg are dependant upon the length of the cable. This thesis discusses the Elastically Loaded Scissors (ELS) Mechanism, which is a variant of the SLP and its application in the actuation of a bio-inspired robotic leg. Driven by ’pulling’ onto the proximal joint of the scissors as opposed to the distal joint, this proposed leg utilizes the increased mechanical advantage of the scissors mechanism to ’amplify’ input angles to larger output displacement by the knee joint. Analysis and Simulations reveal that the proposed mechanism operates in a larger range of motion as compared to the SLP mechanism. However, the amplified motion comes at the cost of higher torque requirements of the knee actuator. However, as the proposed mechanism is tendon actuated, loading due to the weight of the robot decouple the actuator and shift the load onto the parallel elastic components in a gravity compensation configuration. The claims made are validated by experimentation using motion capture and power consumption measurement techniques of the SLP and ELS configurations in a physical quadruped robot.